This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2002-004434 filed in JAPAN on Jan. 11, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a method of producing a gallium nitride (GaN) type 3-5 group compound semiconductor, and to a semiconductor element using the same.
2. Description of the Related Art
A GaN type 3-5 group compound semiconductor represented by the general formula InxGayAlzN (x+y+z=1, 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, and 0xe2x89xa6zxe2x89xa61) can be used as a material for an efficient light emitting device ranging from ultraviolet to visible region, since direct transition type band-gap energy can be adjusted by changing the composition of group 3 elements, so as to correspond to the optical energy of from red to ultraviolet wavelength. Further, such a 3-5 group compound semiconductor has a larger band gap than conventionally-used typical semiconductors such as Si and GaAs and, hence, keeps its semiconductor properties even at such an elevated temperature at which the conventional semiconductors cannot operate. For this reason, the 3-5 group compound semiconductors principally allow the production of electronic devices having superior environmental resistances.
However, such a compound semiconductor is difficult to grow into a large crystal because of its very high vapor pressure at around its melting point. For this reason, there has so far not been obtained a large crystal of such a compound semiconductor for practical use as a substrate to be used in the production of a semiconductor device. Thus, a compound semiconductor of this type, in general, is produced by allowing the compound semiconductor to epitaxially grow on a substrate of a material, such as sapphire or SiC, that is similar in crystal structure to the compound semiconductor and capable of providing a large crystal. At present, a relatively high-quality crystal of the compound semiconductor can be obtained by this method. Even in this case, it is difficult to reduce crystalline defects resulting from the difference in lattice constants or thermal expansion coefficients between the substrate material and the compound semiconductor and the resulting compound semiconductor generally has a defect density of about 108 cmxe2x88x922 or more. In order to produce a highly efficient GaN device, a compound-semiconductor crystal having low dislocation density has been strongly demanded.
Conventionally, a method of decreasing the dislocation density has been developed in a crystal produced by hetero-epitaxial growth method which uses sapphire etc. as a substrate, wherein once a mask pattern is formed on the crystal surface, and then the compound semiconductor is further re-grown. The feature of the method is to grow the compound semiconductor to a lateral direction on the mask, and this method is called Epitaxial Lateral Overgrowth (ELO) Method.
According to the above method, in the early stage of re-growth, crystal growth does not occur on the mask made of, for example, SiO2 etc., but a crystal growth, so-called selective growth, occurs only through opening portions. When the crystal growth is further continued on, the crystal growth through opening portions spreads also on the mask. Thus a buried structure in which the mask is embedded is formed, and finally a flat crystal surface can be obtained. By forming the above buried structure, dislocation density in the re-grown layer can be reduced drastically compared with that in the underlying crystal.
In case of gallium nitride type 3-5 group compound semiconductor, when the above ELO method is applied, generally, a crystal growth is carried out with using c-plane as the surface, and the stripe direction of the stripe mask is generally set to  less than 1-100 greater than  direction, in order to carry out efficiently the lateral direction growth on the mask. However, although depending on the material used as a mask, by ELO method, it has been known that the direction of c-axis of the crystal growth on the mask is misaligned from the c-axis of the underlying crystal. And in the coalescence portions of the misaligned c-axis regions, concentrated dislocation portions called a small angle tilt boundary are generated.
Thus, in the conventional ELO where the mask stripe is set to  less than 1-100 greater than  direction, the direction of c-axis of GaN crystal grown on the mask misalignes from the c-axis of the underlying crystal, and a lot of dislocations occur in GaN layer grown on the mask. It is a big reason why the quality of the obtained 3-5 group compound semiconductor is deteriorated.
The object of the present invention is to provide a method of producing a 3-5 group compound semiconductor and a semiconductor element which can solve the above problem in the conventional technology.
The present invention provides: a method for producing a 3-5 group compound-semiconductor in which a small angle tilt boundary produced in the production of the 3-5 group compound semiconductor by a lateral direction selective growth using stripe mask is reduced in order to produce a 3-5 group compound-semiconductor of high quality and low dislocation density; and a compound-semiconductor using thereof. In order to realize the above, the fluctuation of c-axis of the 3-5 group compound semiconductor which grows thereon is reduced by rotating slightly the mask stripe direction of the mask pattern for a lateral direction selective growth from the predetermined direction, thereby, a small angle tilt boundary is reduced.
That is, in the method of producing the 3-5 group compound semiconductor carrying out the lateral direction selective growth of the desired GaN type 3-5 group compound-semiconductor layer on this c-plane by the stripe mask formed on the c-plane of the underlying crystal containing a GaN type 3-5 group compound semiconductor, a stripe mask is formed on the underlying crystal such that the direction of the stripe is rotated 0.095 or more and less than 9.6xc2x0 from  less than 1-100 greater than  direction, and with using this stripe mask, the lateral direction selective growth of the GaN type 3-5 group compound-semiconductor layer is carried out.
As above, by rotating the stripe direction of the stripe mask used for a lateral direction selective growth within the above range from predetermined  less than 1-100 greater than  direction, the fluctuation of c-axis of the desired compound-semiconductor layer which grows selectively to lateral direction on the c-plane of the underlying crystal is reduced. Consequently, a small angle tilt boundary produced in the desired compound-semiconductor layer decreases, and a high quality 3-5 group compound-semiconductor layer can be formed on the underlying crystal.